(Bloomberg) -- The UK is providing long-range Storm Shadow cruise missiles to help Ukraine counter Russian offensives, Defence Secretary Ben Wallace said.

Wallace told the House of Commons on Thursday that the new weapons will give Ukraine its “best chance” of defending itself against Russian aggression. The UK decision was prompted by Russia’s continuing attacks on Ukrainian civilians, he said.

“We simply will not stand by while Russia kills civilians,” Wallace said. “This is a calibrated and proportionate response to Russia’s escalations.”

The weapons, which were jointly developed by the UK and France, have a firing range in excess of 250 kilometers (155 miles) and are the longest-range missiles yet provided to Ukraine by western allies. The country has been mired in a 15-month war since Russian President Vladimir Putin ordered an invasion in Feb. 2022. 

Confirmation of the missile deployment came after Ukrainian President Volodymyr Zelenskiy told the BBC in an interview that his country needed more time before launching an offensive to recapture lost territory. 

Wallace said that the Storm Shadows, which are usually launched from the air, would be used to push back Russian troops “within Ukrainian sovereign territory.” The UK was given assurances that they would not be used against targets inside Russia, according to a person familiar with the matter. CNN earlier reported the development.

Compatibility Concerns

The front line in Ukraine has remained largely stable for months, with Russia centering its efforts on attempts to capture towns in the eastern Donetsk region, most notably Bakhmut. 

Douglas Barrie, senior fellow for military aerospace at the International Institute for Strategic Studies, a London-based think tank, said the missiles have the potential to increase the ability of Ukraine’s air force to engage long-range targets on the ground. 

“This will allow missile strikes deep into Russian-occupied territory inside the Ukraine, while reducing the risk to the launch aircraft,” Barrie said. He added that the decision was likely under consideration for some time, given the need to address “integration challenges.” 

Speaking in Parliament, Wallace noted Ukraine will need to use the “fourth generation” weapons on Soviet-era Ukrainian aircraft, adding that it may take up to a month to see whether the move makes a difference.

(Updates with detail throughout.)

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